Look on your county records. It will have when it was built, number of bedrooms, square footage of house, garage or outbuildings, etc. Unless the bedrooms upstairs have egress (escape), sufficient light and heat, room size and headroom per code, they may not be listed as such. The savvy buyer will check here, to see if the work was permitted or not. Reduce or increase the house cost.
Ask your local Building Department about upgrading to codes or not. Sloped ceilings- min. 50% at 7' or greater ceiling and areas under 5' high do not count towards required min. floor area. 70 square foot min. with 7' measurement one way.
Be safe, G